Health and Human Services Secretary Kathleen Sebelius demonstrates how to cough Sept. 8, 2009, in Philadelphia. Officials recommend coughing into an elbow instead of a hand to prevent the spread of germs. / Matt Rourke, AP

by Kim Painter, Special for USA TODAY

by Kim Painter, Special for USA TODAY

How long-lasting is the typical cough - the kind you get with a cold? If you guessed about a week, you are average, but you are wrong.

In a new study, doctors who reviewed medical studies found that "acute cough," sometimes called "acute bronchitis," lasts an average of nearly 18 days. But when the doctors asked 493 adults in Georgia how long they expected such coughs to last, estimates averaged seven to nine days.

That mismatch between reality and expectations may be one big reason that so many people wrongly believe that coughs lingering more than a few days need to be treated with antibiotics, says lead researcher Mark Ebell, a family physician and associate professor of public health at the University of Georgia. The report was published Monday in the Annals of Family Medicine.

"I frequently see patients who come in and have been sick for four or five days and say 'boy I really need an antibiotic - I'm just not getting better,' " Ebell says.

In fact, he and other experts say, most acute coughs are caused by viral illnesses, such as colds and flu, and won't be helped by antibiotics no matter how long they last. That's because antibiotics only treat bacterial illnesses, such as some forms of pneumonia. When they are used for viral illnesses, they can do more harm than good - frequently causing diarrhea, allergic reactions and other side effects and spurring the growth of antibiotic-resistant bacteria that can sicken not only the person who took the antibiotics but other people, as well.

Yet, many patients demand the medications and many doctors prescribe them, sometimes just to please patients and save time, says Gustavo Ferrer, a pulmonologist at Cleveland Clinic Florida, in Weston.

"I see it all the time," he says. "Here in Florida, a lot of patients call the urgent care centers Z-Pac clinics," he says, after the antibiotic Zithromax. "They go in with a cough and if the doctors don't prescribe it, they go clinic shopping until they find it."

When that happens, Ebell says, patients often credit the antibiotic for making them feel better a few days later - but "it would have happened anyway." Just letting more patients know how long normal coughs last might help, he says.

Educational efforts aimed at patients and doctors have so far had limited success, according to studies, including one published online Monday in the journal JAMA Internal Medicine. In the study, researchers followed 33 medical practices, including 11 that used printed brochures and posters and 11 that used computerized guidelines to discourage antibiotic use for coughs. Results: Prescription rates dropped from 80% to 68% in the first group and from 74% to 61% in the second.

Those numbers were lower than those at practices that did nothing, but still way too high, says lead researcher Ralph Gonzales, a professor of medicine at the University of California, San Francisco. But he says some individual doctors made bigger changes and he has hopes that a mix of approaches can chip away at the problem. He says he likes Ebell's idea of emphasizing normal cough duration and already uses it: "I tell my patients that I can almost guarantee you will be coughing for a week and that there's an 80 or 90% chance it will be over by three weeks."

Patients who want some temporary relief might try an old-style sedating antihistamine to clear up their post-nasal drip, a big contributor to common coughs, says Melvin Pratter, a professor of medicine at Cooper Medical School of Rowan University in Camden, N.J. Unfortunately, he says, cough syrups and drops are unlikely to help much.

Those who develop possible signs of pneumonia, such as shortness of breath or getting sicker after a partial recovery, should get medical attention, Ebell says.